The present invention relates to the production of outer packaging material and more particularly to the production of such packaging material finished on a printing press.
Outer packaging material is generally understood in the industry to comprise wrappers, carriers and the like for primary containers such as bottles or cans. Most outer packaging material is made of paper, or paperboard, typically referred to as folding carton material or corrugated paperboard. Unbleached paperboard is specifically manufactured to be used for outer container packaging. High strength is desired, so the board is usually produced from strong fiber and contains chemical additives to resist moisture. After the board is made, it has been the custom in the industry to finish at least one surface with a white coating or the like, to permit printing of the naturally brown, rough surface of the unbleached board. One method has been to coat one surface of the board in an on or off machine coating process with a coating composition comprising latex, clay and titanium dioxide. In other cases, an outer thin layer of high-quality label paper or a plastic film have been laminated to one surface of the unbleached paperboard to provide a printable surface.
Containers of two types employ white surfaced (clay coated) unbleached kraft board. The first type are corrugated packages. In the manufacture of white top corrugated packages, the outer surface of a sheet of linerboard (for example, about 30-65 lbs./1000 square feet basis weight) is clay coated at the paper mill, pre-printed in web form by flexography with high quality graphics, then used as the outer liner in the corrugating process before being converted into boxes. The second type are single ply folding cartons such as beverage carriers. For these packages, the unbleached paperboard (for example, about 40-100 lbs./1000 square feet basis weight) is coated at the paper mill, printed by gravure, die-cut and converted directly into boxes. The board used for the second type of packages needs to be heavier and stiffer than the board used in the first type. At the present time the heavier weight clay coated board is in short supply and thus is expensive. Meanwhile the lighter weight coated linerboard for corrugated boxes is no longer extensively made in the United States since it requires specialized facilities for its production which generally aren't available at a kraft mill. For this reason, more and more users have switched to the more expensive laminated products using plastic films and label paper.